Electrohydrodynamic Conduction Driven Single- and Two-Phase Flow in Microchannels With Heat Transfer

2013 ◽  
Vol 135 (10) ◽  
Author(s):  
Matthew R. Pearson ◽  
Jamal Seyed-Yagoobi
Keyword(s):  
Heat Transfer ◽  
Transport Process ◽  
Heat Fluxes ◽  
Phase Flow ◽  
Reverse Effect ◽  
Two Phase ◽  
Small Areas ◽  
Dielectric Liquids ◽  
Phase Loop ◽  
Heat Transport Process

Microchannels have well-known applications in cooling because of their ability to handle large quantities of heat from small areas. Electrohydrodynamic (EHD) conduction pumping at the microscale has previously been demonstrated to effectively pump dielectric liquids through adiabatic microchannels by using electrodes that are flushed against the walls of the channel. In this study, an EHD micropump is used to pump liquid within a two-phase loop that contains a microchannel evaporator. Additional EHD electrodes are embedded within the evaporator, which can be energized separately from the adiabatic pump. The effect of these embedded electrodes on the heat transport process, flow rate, and pressure in the micro-evaporator and on the two-phase loop system is characterized. Local enhancements are found to be up to 30% at low heat fluxes. The reverse effect that phase-change has on the EHD conduction pumping phenomenon is also quantified.

Single- and Two-Phase Flow in Microchannels With Heat Transfer and Driven by an EHD Conduction Pump

2011 ◽  
Author(s):  
Matthew R. Pearson ◽  
Jamal Seyed-Yagoobi
Keyword(s):  
Heat Transfer ◽  
Transport Process ◽  
Enhancement Effect ◽  
Phase Flow ◽  
Two Phase ◽  
Small Areas ◽  
Dielectric Liquids ◽  
Phase Loop ◽  
Two Phase Heat Transfer ◽  
Heat Transport Process

Microchannels have well-known applications in cooling because of their ability to handle large quantities of heat from small areas. Electrohydrodynamic (EHD) conduction pumping at the micro-scale has previously been demonstrated to effectively pump dielectric liquids through adiabatic microchannels by using electrodes that are flushed against the walls of the channel. In this study, an EHD micropump is used to pump liquid within a two-phase loop that contains a microchannel evaporator. Additional EHD electrodes are embedded within the evaporator, which can be energized separately from the adiabatic pump. The enhancement effect of these embedded electrodes on the heat transport process in the micro-evaporator and on the two-phase loop system is characterized. Single- and two-phase heat transfer regimes are both studied and the effect of applied voltage and heat flux are considered on the overall flow rate and the wall temperature of the microchannel.

IR Based Inverse Calculation of Two-Phase Heat Transfer Coefficients in Microgap Channels

2011 ◽  
Author(s):  
Jessica Sheehan ◽  
Avram Bar-Cohen
Keyword(s):  
Heat Transfer ◽  
Mass Flux ◽  
Heat Fluxes ◽  
Heated Wall ◽  
Phase Flow ◽  
Ir Thermography ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Heat Transfer Coefficients ◽  
Two Phase Heat Transfer

IR thermography of the heated wall for the two-phase flow of FC-72 in microgap channels provides explicit evidence of the quality-driven M-shaped variations in the two-phase microgap heat transfer coefficients. Data obtained from a 210μ microgap channel, operated with an FC-72 mass flux of 195 and 780 kg/m2-s and asymmetric heat fluxes of 28 W/cm2 to 35 W/cm2 are presented and discussed.

Computational Method for Characterization of a Microchannel Heat Sink Involving Two-Phase Flow

2005 ◽  
Author(s):  
Kanchan M. Kelkar ◽  
Suhas V. Patankar ◽  
Sukhvinder Kang
Keyword(s):  
Heat Transfer ◽  
Heat Sink ◽  
Two Phase Flow ◽  
Phase Region ◽  
Heat Fluxes ◽  
Computational Method ◽  
Phase Flow ◽  
Microchannel Heat Sink ◽  
Two Phase ◽  
Solid Region

Microchannel heat sinks are being increasingly considered for the cooling of electronic equipment because of their ability to absorb high heat fluxes directly from the heat-dissipating components in a compact manner with a low thermal resistance. In this study, a computational method is presented for the analysis of conjugate heat transfer and two-phase flow in a heat sink containing a single microchannel. It involves a two-domain solution of the three-dimensional conduction within the solid region and the one-dimensional two-phase momentum and energy transfer within a microchannel. The nonlinear coupling between the two domains that occurs through the heat exchange at the walls of the microchannels is handled using an iterative calculation. Analysis of the flow and heat transfer in the microchannel is based on the homogenous flow assumption that is deemed to be accurate for the flow of low surface tension coolants such as methanol, isobutane, and HFC’s. Representative single and two-phase correlations are used for the calculation of the friction factor and the heat transfer coefficient. The computational model is applied for the prediction of the performance of a microchannel heat sink over a range of mass flow rates. The results of the analysis show the important physical effects that govern the performance of the microchannel heat sink involving two-phase flow. These include the acceleration of the flow in the microchannel in the two-phase region that influences the pressure drop through it and the two-phase enhancement of heat transfer that determines the temperature field within the solid region.   This paper was also originally published as part of the Proceedings of the ASME 2005 Heat Transfer Summer Conference.

Modeling and Prediction of Two-Phase Refrigerant Flow Regimes and Heat Transfer Characteristics in Microgap Channels

2007 ◽  
Author(s):  
Avram Bar-Cohen ◽  
Emil Rahim
Keyword(s):  
Heat Transfer ◽  
Annular Flow ◽  
Two Phase Flow ◽  
Flow Regimes ◽  
Phase Flow ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Channel Diameter ◽  
Dielectric Liquids ◽  
Transition Criteria

This keynote lecture will open with a brief review of the primary two-phase flow regimes and their impact on thermal transport phenomena in tubes and channels. The Taitel and Dukler flow regime mapping methodology will then be described and applied to the two-phase flow of refrigerants and dielectric liquids in microgap channels. The effects of channel diameter, as well as alternative transition criteria, on the prevailing flow regimes in microgaps will be explored along with available criteria for microchannel behavior. Available microgap data will then be shown to reflect the dominance of annular flow and to display a characteristic heat transfer coefficient curve in such configurations. It is found that the heat transfer coefficients in the low-quality annular flow segment of this locus can be predicted by available, microtube correlations, but that the moderate-quality transition to the axially-decreasing segment occurs at substantially.

Heat Transfer Mechanism and Flow Pattern During Flow Boiling of Water in a Vertical Narrow Channel: Experimental Results

2006 ◽  
Author(s):  
Ewelina Sobierska ◽  
Rudi Kulenovic ◽  
Rainer Mertz
Keyword(s):  
Heat Transfer ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Heat Fluxes ◽  
Transfer Mechanism ◽  
Phase Flow ◽  
Fluid Temperature ◽  
Heat Transfer Mechanism ◽  
Two Phase ◽  
Mass Fluxes

Experimental investigations on flow boiling phenomena in a vertical narrow rectangular microchannel with the hydraulic diameter dh = 0.48 mm were carried out. The experiments were performed under fluid-inlet subcooling conditions with deionised and degassed water for different mass fluxes. Investigations on pressure drop and heat transfer during single-and two-phase flow have been carried out. Moreover, flow visualisation of the two-phase flow patterns along the channel was performed using a digital high-speed video camera. The present work outlines local heat transfer coefficients for three mass fluxes (200, 700 and 1500 kg/m2s) and heat fluxes (30–110, 35–150 and 65–200 kW/m2, respectively) during two-phase flow. The fluid temperature at the inlet was about 50 °C what corresponds to inlet subcooling, depending on flow pressure conditions, from 34 °C to 57 °C. The visual observations were used to obtain a better insight about the heat transfer mechanism.

Local Measurement of Forced Convection Heat Transfer in a Micro Glass Tube

2008 ◽  
Author(s):  
B. Schilder ◽  
S. C. M. Yu ◽  
N. Kasagi ◽  
S. Hardt ◽  
P. Stephan
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Indium Tin Oxide ◽  
Single Phase ◽  
Glass Tube ◽  
Heat Fluxes ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Two Phase ◽  
Nusselt Numbers

The pressure drop and the convective heat transfer characteristics of ethanol and water in a 600 μm diameter tube with and without phase change has been studied experimentally. The test section consists of a glass tube coated with a transparent ITO (indium tin oxide) heater film. For single phase flow it was found that the measured Nusselt numbers and friction factors are in good agreement with the theoretical values expected from Poiseuille flow. Subsequently, the boiling heat transfer of ethanol was studied. It was found that boiling with bubble growth in both upstream and downstream directions leaving behind a thin evaporating liquid film on the tube wall is the dominant phase change process. Local Nusselt numbers are calculated for the two phase flow at different heat fluxes and Reynolds numbers. Compared to single phase flow the heat transfer is enhanced by a factor of 3 to 8.

Experimental Investigation of Flow Boiling in a Vertical Narrow Channel

2005 ◽  
Author(s):  
Ewelina Sobierska ◽  
Klaudia Chmiel ◽  
Rudi Kulenovic ◽  
Rainer Mertz
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Heat Fluxes ◽  
Experimental Investigations ◽  
Flow Visualisation ◽  
Phase Flow ◽  
Two Phase

Experimental investigations on thermofluid-dynamic phenomena in a vertical narrow rectangular microchannel with the hydraulic diameter dh = 0.27 mm were carried out. The experiments are performed under fluid-inlet subcooling conditions with de-ionised and degassed water for different mass fluxes (50–2000 kg/m2s) and heat fluxes (2–150 kW/m2). Moreover, flow visualisation of the two-phase flow patterns along the channel is performed using a digital high-speed video camera. Investigations on pressure drop during single- and two-phase flow have been carried out. The present work is concentrated on two-phase heat transfer. The mean heat transfer coefficient and the local heat transfer coefficient at saturated conditions were calculated and the latter ones was compared with available correlations.

Two-Phase Flow and Heat Transfer in Pin-Fin Enhanced Micro-Gaps With Non-Uniform Heating

2013 ◽  
Author(s):  
Steven A. Isaacs ◽  
Yogendra Joshi ◽  
Yue Zhang ◽  
Muhannad S. Bakir ◽  
Yoon Jo Kim
Keyword(s):  
Heat Transfer ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Phase Flow ◽  
Two Phase ◽  
Pin Fin ◽  
Flow And Heat Transfer ◽  
Imaging Results

In modern microprocessors, thermal management has become one of the main hurdles in continued performance enhancement. Cooling schemes utilizing single phase microfluidics have been investigated extensively for enhanced heat dissipation from microprocessors. However, two-phase fluidic cooling devices are becoming a promising approach, and are less understood. This study aims to examine two-phase flow and heat transfer within a pin-fin enhanced micro-gap. The pin-fin array covered an area of 1cm × 1cm and had a pin diameter, height and pitch of 150μm, 200μm and 225μm, respectively, (aspect ratio of 1.33). Heating from two upstream heaters was considered. The working fluid used was R245fa. The average heat transfer coefficient was evaluated for a range of heat fluxes and flow rates. Flow regime visualization was performed using high-speed imaging. Results indicate a sharp transition to convective flow boiling mechanism. Unique, conically-shaped two-phase wakes are recorded, demonstrating 2D spreading capability of the device. Surface roughness features are also discussed.

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